The role of soils and crops in water yield

The objectives of this study were (1) to determine soil moisture differences within and among soils, and (2) to determine the effect of the crop grown upon the soil moisture regime. Two small watersheds, W-5 (12.2 acres) and W-8 (9.3 acres) located on the Middle Tennessee Agricultural Experiment Station, Springhill, Tennessee, and Milan Field Station, Milan, Tennessee, respectively, were chosen for this study. Seventeen soil moisture sites, with three moisture tubes per site, were selected to represent twelve soil mapping units on the two watersheds. Moisture measurements were made approximately biweekly from May through December 1967. Yield data of the corn on W-3 were recorded on a dry matter basis. Data representing maximum and minimum observed moisture levels at each site were depicted graphically and analyzed relative to the surrounding soil conditions, soil type, slope position, bulk density, and textural classifications, one moisture tube was selected, on the basis of homogeneity of surrounding conditions, to represent each soil on W-5 and W-8, and soil moisture depths within specific soil depth zones were plotted against time of observation. The following conclusions were delineated from this study: 1. Conditions such as depressions, plow furrows, and vegetative growth adjacent to the soil moisture access tubes greatly affect moisture readings. 2. Soils located at the base of slopes, where frequent ponding occurred, had wider moisture ranges than the surrounding soils on the slopes. 3. Soil horizons having high bulk density, especially in pan layers, restricted percolation and tended to support moisture above them. 4. The soils which were highest in clay content tended to have narrower moisture fluctuation ranges. 5. The greatest hydrologic activity occurred within soils at the 0 to 15 inch depth. 6. Greater soil moisture deficits occurred in soils when the access tubes were surrounded by corn rather than by grass and weeds.